Vector Polarization Analysis on DNS

Schweika, W.; Easton, S.; Neumann, K.‐U.

doi:10.1080/10448630500454262

Cited by 4 publications

(4 citation statements)

References 7 publications

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“…General polarization analysis may be carried out using socalled neutron polarimetry or vector polarization analysis in which not only the polarized neutron cross sections are measured but also the rotation angle of the neutron polarization (Brown et al, 1993). However, it has, up to now, proved difficult to implement the technique of neutron polarimetry on multi-detector spectrometers (Schweika et al, 2005).…”

Section: Limitations Of Xyz-polarization Analysismentioning

confidence: 99%

Disordered materials studied using neutron polarization analysis on the multi-detector spectrometer, D7

Stewart¹,

Deen²,

Andersen³

et al. 2008

J Appl Crystallogr

160

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The technique of longitudinal neutron polarization analysis on a multi-detector neutron spectrometer (so-called 'xyz'-polarization analysis) is presented. This technique allows the simultaneous and unambiguous determination of the nuclear, magnetic and nuclear spin-incoherent scattering cross sections as a function of both momentum transfer and energy transfer. The implementation of xyz-polarization analysis on the recently upgraded D7 spectrometer at the Institut Laue-Langevin in Grenoble is described. Several examples of neutron polarization analysis studies of disordered systems on D7 are given, illustrating the valuable information which can be retrieved from the analysis of neutron diffraction patterns between the Bragg peaks. ‡ Current address: ISIS Facility, Rutherford Appleton Laboratory, Didcot, UK. research papers J. Appl. Cryst. (2009). 42, 69-84 J. R. Stewart et al. Disordered materials studied using neutron polarization analysis 71 research papers 80 J. R. Stewart et al. Disordered materials studied using neutron polarization analysis

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Section: Limitations Of Xyz-polarization Analysismentioning

confidence: 99%

Disordered materials studied using neutron polarization analysis on the multi-detector spectrometer, D7

Stewart¹,

Deen²,

Andersen³

et al. 2008

J Appl Crystallogr

160

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“…The scattering experiments were performed on the DNS instrument in Jülich. In contrast to most previous investigations [14,15,17], the magnetic scattering was separated from nuclear scattering by polarization analysis [16,25]. A fortiori, the separated high background due to nuclear spin-incoherent scattering from Co serves as an intrinsic calibration of the paramagnetic cross-section; a procedure that avoids usual systematic errors and corrections.…”

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confidence: 99%

Approaching the Ground State of the Kagomé Antiferromagnet

2007

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Y 0:5 Ca 0:5 BaCo 4 O 7 contains kagomé layers of Co ions, whose spins are strongly coupled, with a CurieWeiss temperature of ÿ2200 K. At low temperature, T 1:2 K, our diffuse neutron scattering study with polarization analysis reveals characteristic spin correlations close to a predicted two-dimensional coplanar ground state with staggered chirality. The absence of three-dimensional long-range antiferromagnetic order indicates negligible coupling between the kagomé layers. The scattering intensities are consistent with high spin S 3=2 states of Co 2 in the kagomé layers and low spin S 0 states for Co 3 ions on interlayer sites. Our observations agree with previous Monte Carlo simulations indicating a ground state of effectively short range, staggered chiral spin order. DOI: 10.1103/PhysRevLett.98.067201 PACS numbers: 75.25.+z, 61.12.ÿq, 75.40.Cx, 75.50.Ee The topology of many crystal structures has an important influence on the collective behavior of interacting magnetic moments. In lattices with triangular networks the antiferromagnetic (AF) coupling between all spins cannot be satisfied simultaneously owing to geometrical frustration that strongly reduces the ordering temperature and disturbs the settling of the system into a long-range ordered state. Exotic phenomena such as spin-ice and spinliquid phases can emerge from magnetic interactions that are incompatible with the underlying crystal geometry. A hallmark of frustration is the large degeneracy of complex, noncollinear ground states of finite entropy and the appearance of chiral correlations [1]. According to the MerminWagner theorem [2], in low dimensions, the AF order that would reveal the ground state properties is suppressed at finite temperatures. The famous case of spins on the twodimensional kagomé lattice that are simply AF coupled to only nearest neighbor comprises high geometrical frustration and low dimensionality and still challenges theoretical understanding as well as experimental observations and analysis.Here, we present diffuse neutron scattering results with polarization analysis on a new compound Y 0:5 Ca 0:5 BaCo 4 O 7 , in which the Co spins (S 3=2) in noninteracting kagomé layers appear to realize ideally the kagomé AF with only 2D nearest neighbor interactions, which allows an unprecedented approach to its unusual ground state properties.Considering the classical Heisenberg model of AF coupled nearest neighbor spins on the kagomé lattice, the ground state is highly degenerate and characterized by competing chiral spin structures. The spins have a relative orientation of 120 degrees in each triangular unit, so that the local sum of spins is zero. However, there are two competing structures that show either uniform or staggered chirality, see Fig. 1. According to predictions for the classical Heisenberg AF the staggered chiral structure is favored [3,4], because the existence of local zero energy modes, so-called weathervane defects, which are common spin rotations on hexagons, cause a larger degeneracy; such entropical selecti...

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“…( 7) also reveal the mentioned interference terms. It should be noted that the same XYZ-setup for multi-detectors can be used to access the complete polarisation tensor and off-diagonal terms can be determined with the same accuracy by spherical neutron polarimetry with precessing incident polarization [17,18]. However, the here proposed XYZ-polarisation analysis, a method based on only diagonal terms and applicable for multi-detectors, will certainly provide a much more convenient and efficient separation for the diffuse magnetic neutron scattering from single crystals.…”

Section: Final Remarksmentioning

confidence: 99%

XYZ-polarisation analysis of diffuse magnetic neutron scattering from single crystals

Schweika

2010

J. Phys.: Conf. Ser.

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Studies of diffuse magnetic scattering largely benefit from the use of a multi-detector covering wide scattering angles. Therefore, the different contributions to the diffuse scattering that originate from magnetic, nuclear coherent, and nuclear spin-incoherent scattering can be separated by the so-called XYZ-polarization analysis. In the past this method has been successfully applied to the analysis of diffuse scattering by polycrystalline samples of magnetic disordered materials. Single crystal studies that exploit the vector properties of spin correlations are of particular interest for furthering our understanding of frustration effects in magnetism. Based on the symmetry properties of polarised scattering a suitable extension of the conventional XYZ method has been derived, which allows for the complete separation and the analysis of features of diffuse magnetic scattering from single crystals.

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Vector Polarization Analysis on DNS

Cited by 4 publications

References 7 publications

Disordered materials studied using neutron polarization analysis on the multi-detector spectrometer, D7

Disordered materials studied using neutron polarization analysis on the multi-detector spectrometer, D7

Approaching the Ground State of the Kagomé Antiferromagnet

XYZ-polarisation analysis of diffuse magnetic neutron scattering from single crystals

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